LCGB Forums

Hi, I'm rebuilding an '83 Spanish SX200 with the original Motoplat Electronic flywheel on a Slim/LI taper crank and the heavy flywheel. I am sticking with the standard cylinder set up but will hone slightly and replace piston. Probably move to a slightly bigger carb (25mm) and modern exhaust.

Question is - is it common for the crank/flywheel to sheer on this set up due to the flywheel weight or should be OK as long as I dont put a performance kit on ?

GP Crank and Flywheel/Stator ~£400, only worth doing this if there is historic problems with this set-up.

Yes, there is a risk of you shearing the taper off the crank. This question has been asked a hundred time or more online, including on here, so you should be able to bore yourself to sleep with the amount of info you'll find, with opposing opinions.

Not only do I have first-hand experience of at least 4 failures but I often respond to this question by sharing my most recent example, which was talking about it with Jaime Supereibar at the French Euro Lambretta, only for him to say that it was evident that the factory bikes had exactly this failure in the 1980s endurance race footage that he was about to show at said rally.

Nobody can tell you that your bike will or will not suffer this failure but there are plenty of examples of both, including Spanish factory bikes, of all CCs, and whether fitted with the Motoplat points or electronic systems. However, the bigger the CC = the greater the chance. The chance is also higher when fitted with the heavier electronic system.

You stick with a heavy flywheel on a weak crank taper... you take your chances.

Personally, I have upgraded by either changing to stronger GP crank and ignition or by changing my ignition to a lighter flywheel and retaining the weaker type crank. Dave Webster stated that you could race on these cranks, providing your flywheel was light enough.

All the best, regardless of which way you choose to go.

Adam